1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a fiber reinforced plastic structure that can be applied to a large structure such as an aircraft body, a vessel, a rail vehicle, and a windmill blade.
2. Description of the Related Art
Usage of fiber reinforced plastic (FRP) now ranges over various fields. A carbon fiber rod is suitably used for a fishing rod and a golf putter. A multilayer fiber reinforced plastic is suitably used for a vessel body such as a boat and a yacht. A fiber reinforced plastic having properties of being light weight and highly strong has recently been desired to be used for a large structure such as an aircraft body and a windmill blade.
For ensuring the strength and stable physical properties of this type of fiber reinforced structure, it is important to prevent entrance of foams into a fiber reinforced plastic or generation of air holes therein during manufacturing processes. In a method of flowing fluid plastic into a fiber laminate laid in a mold and impregnating the fluid plastic in the fiber layer, air holes may be generated in the plastic layer. A vacuum forming method disclosed for example in Japanese Patent Application Laid-open No. 60-83826 is known as a technique of preventing generation of air holes in a layer.
In the technique disclosed in Japanese Patent Application Laid-open No. 60-83826, vacuuming is performed on one side of a mold cavity closed by an inner surface of a mold and a vacuum film, and fluid plastic is injected from the other side. Air in the cavity is replaced with the fluid plastic, and whereby a fiber reinforced plastic structure with less foams and air holes is manufactured.
An improvement in a vacuum forming technique is necessary for this technique for distributing and allocating fluid plastic spatially uniformly to a fiber layer. Examples of such an improvement include techniques disclosed in U.S. Pat. Nos. 4,902,215 and 5,904,972.
The known techniques have in common that, as shown abstractly and schematically in FIG. 7, a plastic flow medium 103 such as a structure having grid holes, especially a nylon net, is laid on the side of the top surface of a plastic laminate 106 in a cavity formed by a mold 101 and a vacuum film 102, and as shown in FIG. 8, fluid plastic 105 is injected from a number of holes opened on a plastic injection hose 104, vacuuming 107 is performed from the edge of the cavity, and the plastic percolates the grid meshes of the plastic flow medium 103 to be impregnated to a fiber laminate 106 of the base layer. The plastic flow medium 103 is used for achieving two-dimensional diffusion uniformity of fluid plastic.
When a thick FRP product is manufactured by this technique, it is difficult to make the flow rate uniform. As shown in FIG. 8, because the fluid plastic does not flow uniformly, an unimpregnated site 108 in which no plastic is impregnated to a fiber laminate is prone to be generated, and impregnation defects are likely to occur.
Therefore, it is demanded to suppress generation of impregnation defects by improving fluidity and diffusability of an injected plastic simultaneously. It is accordingly desired to shorten a manufacturing cycle by increasing a plastic injection rate.
When the plastic flow medium 103 is used, there is a difference in diffusability of an injected plastic that flows near the plastic flow medium 103 and that flows on the side of the mold 101, and it is desired to suppress generation of impregnation defects by resolving the difference. Especially, in manufacturing a thick or a long large structure, unimpregnated parts are generated frequently. Therefore, it is desired to prevent generation of unimpregnated parts.
In view of the problems, an object of the present invention is to provide an apparatus and a method for manufacturing a fiber reinforced plastic structure that can solve generation of impregnation defects.